The SCA TECHNICAL PRIMER for RADIO TALKING BOOK Engineering Fact and Opinion By: ROBERT D. WATSON Copyright Release Notice: The entire contents of this work have been made available to Minnesota State Services for the Blind and Visually Handicapped, and to the Association of Radio Reading Services for their use and distribution by the author. "THE SCA TECHNICAL PRIMER FOR RADIO TALKING BOOK" is the copyrighted work of the author, Robert D. Watson. You are granted a limited license to use and copy this work for distribution subject to the following conditions: 1. No fees may be charged for such copying and distribution. 2. This work may only be distributed in its original, unmodified form. 3. Contributions for the use of this work will be appreciated, and will be forwarded to the Association of Radio Reading Services to further its efforts on behalf of blind and visually handicapped people. About the Author: Robert D. Watson, Sr. Engineer and Supervisor of Engineering for Minnesota State Services for the Blind first joined the state agency in 1956 and established the technical facilities to record materials and distribute them to blind residents of the state. That facility has grown, and today is known as the "Communication Center". Mr. Watson has been involved in broadcast and communication electronics since 1950. He holds the both First-Class Radiotelephone and amateur ("Ham") Extra-Class FCC licenses. In 1958 he accepted assignments with the U.S. Navy submarine service, specializing in radar electronics and nuclear power reactor control systems. In 1964 he accepted a position as a research and development engineer with the Honeywell Aero-Space division, where he was involved with the Gemini, Apollo, and Manned Orbiting Laboratory space vehicles; and was an engineering consultant at the NASA Space Center in Houston, Texas. In 1967 he volunteered his talents to design a private radio distribution system to serve the blind residents of the state of Minnesota, and in 1969 he returned to a full-time staff position with the state agency to oversee its engineering operations. Bob, his wife Judy and his son Barry live in the picturesque St. Croix river valley near Stillwater, where Bob actively pursues private flying, computing, ham radio, photography, and gardening. TABLE OF CONTENTS Page Introduction & Dedication 4 Chapter 1: WHAT IS "SCA"? 6 (Secret Club Activity?) Chapter 2: SCA TRANSMISSION PARAMETERS 10 (And You Thought Only Doctors Gave Injections?) Chapter 3: SCA AND STEREO COMPATIBILITY 16 (Birdies Should Be Feathered) Chapter 4: SCA PROGRAM STUDIO FACILITIES 22 (Oops, There Goes The Budget!) Chapter 5: MICROPHONES AND TECHNIQUES 35 (Why Your Home Recordings Sound Like Home Recordings!) Chapter 6: STUDIO TO TRANSMITTER LINKS 43 (How To Get There From Here.) Chapter 7: SCA BROADCAST COVERAGE DISTANCE 46 (Can Anyone Out There Hear You?) Chapter 8: OFF-AIR RELAYS AND CABLES 52 (How To Get On-the-Air Where You Aren't.) Chapter 9: COMMERCIAL DEMANDS ON SCA'S 57 (F.C.C. & Others vs RTB) Quadraphonic FM 57 (Does Anyone Really Care?) Utility Load Management 62 (Power Companies Would Like Your Channel!) The Commercialism of Public Radio SCA 63 (What's It Worth To Ya?) Broadcasting Amendments Act of 1981 64 (Governments Good Intentions "Run Amuck") New SCA's Needed 64 (The Common Sense Solution) The FCC Reacts (Nobody's Perfect!) 66 1986 Update and Closing Comments 67 INTRODUCTION Most introduction pages are viewed as "skip this page" drivel by many readers. If you would rather not hear about the agony we suffered learning how to tame the Radio Talking Book SCA, then by all means, advance to the main entre. If you are curious about how we "got here" from nothing back in the late l960's then this is for you. Like most great developments, Radio Talking Book's basic concept was realized by a few people for a long time before someone with the knowledge and insight to make it a practical reality took hold and ran with it. That person was C. Stanley Potter, Administrator of Minnesota State Services for the Blind and Visually Handicapped. When Mr. William Kling, President of what is today "Minnesota Public Radio" (MPR), showed up one day to inquire if we might be interested in using the SCA channel of his new local FM radio station, all the ideas and pieces began to fall into place. Mr. Potter called me to inquire about the technical feasibility of SCA use, since I was a long time acquaintance and friend, and since I also just happened to be an engineer in the Aero-Space industry with a life long background in radio technology. Mr. Daniel Rieder, Mr. Michael Shields, (both of MPR engineering) and myself undertook an extensive study of the technical capabilities of the SCA for speech program uses. Our unanimous conclusion was that the theoretical constraints of use of an SCA were such that it could not provide a viable vehicle for speech program uses. Upon formal presentation of this report to Mr. Potter, he, like other great leaders before him, agreed with the report and then said, "OK, now you guys go make it work". A few days later Dan and I got back together to discuss what to do next. After many additional hours of restudying the calculations and their predictions we realized that there was only one avenue left. "To H... with theory, let's see what we really can do with it!", one of us proclaimed. So we began bench tests, and soon thereafter, on-air-tests. Essentially what we discovered was that speech program material that was mostly from tape recordings done at 3 3/4 inches per second speed, had such a low statistical average of high frequency energy that the nominal modulation level (loudness) of the SCA channel could be much greater than theory would predict and still produce no subjectively detrimental effects upon a listener to the stereo main channel broadcasts of the FM station. It became apparent that the poor signal-to-noise performance of an SCA, and the narrow bandwidth available for use would demand that extensive audio processing control be employed and rigidly adhered to. It was also clearly apparent that the main channel audio modulation must be kept under control, or at least within strict bounds, at all times. No part of the transmission system could be neglected if satisfactory performance was to be realized by both the SCA and main channel. The possible problem sources revealed themselves to us at totally unplanned times over a couple of years. Thus, having our fingers repeatedly slapped, we finally learned to believe in Murphy's Law (If anything can go wrong it will.) and carefully watched all of the details. As a result of concerned and conscientious engineering efforts plus a completely cooperative, non-adversary, relationship between the outstanding engineering talent of Dan and Mike for MPR and the State Services for the Blind agency, Minnesota listeners, for more than 17 years have enjoyed unparalleled "Fine Arts" stereo programming quality while simultaneously, the visually handicapped of Minnesota have received informational programs never previously available anywhere in the world. It hasn't always been easy, sometimes didn't even seem possible, but always it was & is necessary and important to make the SCA program service to the blind a reality. To those devoted few with whom I've had the honor of sharing many of the wee hours over thousands of cups of cold coffee and countless schematics and equations drawn on napkins; and to those of you who study these notes to further this SCA service to more people, I extend my gratitude and the dedication of this paper. Special recognition and deep appreciation is also extended to Ellie Sevdy who volunteered to type this material for me. Her ability to correct my frequent misspellings and decipher whether my strange use of grammar was a personality trait of mine, or meant to be humorous, or was actually just bad grammar should earn her the "Purple Heart" of stenography. Without her assistance this document would not exist. Robert D. Watson